Clinical history

A telephone call was received from an aquarist who was concerned about one of his female Frontosa cichlids.

This female Cyphotilapia frontosa was part of a breeding group consisting of two males and five females. The aquarium was 180 cm × 60 cm × 60 cm. Temperature was 28°C. The pH was 8.1. Ammonia and nitrite were zero. Nitrate was 20 mg/l. C. frontosa are part of the cichlid species flock originating from Lake Tanganyika. They are maternal mouth brooders.

Physical examination

The cichlid was presented in a bucket of water that had been taken from its aquarium. The fish was showing atypical dark marking, probably as a result of the stress of transport.

The fish was netted and the gills briefly examined by alternately lifting the operculae with the fish restrained in the net. A dark mass could be seen associated with the gills on the right hand side (Fig.5.1).

Fig. 5.1 A dark mass can be seen along the leading edge of the first gill arch, flanked by gill rakers at either end.

Clinical diagnosis examination

Examination under anaesthetic

The fish was subsequently examined under anaesthetic. A solution of tricaine methanesulphonate (MS222), dissolved in a saturated solution of NaHCO₃ to form a buffered stock solution of 10 g/l, was used to anaesthetize the fish. This was added incrementally until the cichlid began to show signs of induction, notably loss of the righting reflex.

Once the fish was failing to respond to external stimuli but respiration was still good (as judged by opercular movements), the cichlid was removed from the water and placed on a surface of damp tissue.

Anaesthesia was continued by syringing oxygenated water into the mouth such that it flowed over the gills and out through the operculae. This mimics the physiologically normal direction of water flow so as not to short circuit the normal counter current gaseous exchange mechanism. Anaesthesia was maintained by alternating exposure either to water with MS222 if the fish appeared to be light or without if thought to be on a deep enough plane of anaesthesia.

The mass was examined. It appeared to be larger than initially thought, with the bulk of the mass hidden on the lingual side of the branchial arches (Fig.5.2).

Fig. 5.2 The mass was hidden on the lingual side of the branchial arches.

1. List your differential diagnoses.

Differential diagnoses for gill mass

Therapy

2. What treatment options are available to you?

Treatment options are limited but would include:

It was elected to remove the mass surgically. This was achieved by resection of the first branchial arch. This was clamped at either end and ligated with PDS (Fig.5.3). Antibiotic cover was provided with an intramuscular injection of 1 mg marbofloxacin. Recovery involved placing the cichlid back into water that did not contain MS222.

Fig. 5.3 The mass was surgically removed. This was achieved by resection of the first branchial arch. This was clamped at either end and ligated with PDS.

The mass was some 2.0 cm in diameter and was submitted for histological examination (Fig.5.4).

Fig. 5.4 The mass was 2 cm in diameter and was submitted for histological examination.

Histopathological diagnosis

The removed mass was histopathologically identified as a low-grade spindle cell sarcoma. No evidence for metastasis was noted.

Discussion

Spindle cell sarcomas are a wide group of mesenchymal malignancies that can originate from many different cells of origin and include fibrosarcomas, smooth muscle tumours and peripheral nerve sheath neoplasms. Typically, sarcomas prove to be locally invasive and destructive malignancies, although metastasis is rare. It is interesting here that this tumour also caused incubation difficulties in the previously successful mouth-brooding female. Whether this was a physical problem and she was unable to contain the full volume of the mass and her developing brood in the oral cavity, or whether it was because the mass was already compromising her respiration such that the presence of the brood proved one stressor too far, is unknown.

A variety of gill neoplasms have been recorded including papillomas, squamous cell carcinomas, branchioblastomas and chondromas (Childs and Whitaker 2001). Sarcomas have been well described in a variety of fish (Earnest-Koons etal. 1996, Lewbart etal. 1998, Schmale etal. 2002), although their presence in cichlids does not appear to have been widely reported. In the walleye, dermal sarcomas are due to a retroviral infection and can be transmitted (Earnest-Koons etal. 1996) – interestingly, other sarcomas in fish appear to be linked to viral agents or at least a virus-like agent (Schmale etal. 2002),

Surgical resection in this case should give a satisfactory outcome. There appears grossly to be several millimetres of normal gill tissue on either side of the tumour and, histologically, no evidence of metastasis was noted. No evidence of a viral infection was noted, although this cannot be excluded on histology alone.

Clinical history

Two common goldfish (Carassius auratus) were presented. The owner claimed that two or three fish per day were dying. Over the previous 3 weeks the owner had lost roughly half of his fish.

The pond is a butyl-lined formal pond with rough dimensions of 3 m × 2.5 m × 60 cm deep, and has been there for around 12 years. There are some marginal plants and it is filtered and has an extra pump installed to improve circulation. It held a mixture of goldfish and common carp and losses had been seen in both. The pond had been considered overstocked through natural breeding and so some had been re-homed previously. No new fish had been introduced in the last 2 years. A sample of his pond water had been checked by a local aquatics’ retailer and he was told that it was fine, although he had no idea what had been checked. The water temperature was unknown.

The owner reported that the fish were trying to feed but were not ingesting the food; some were sluggish, some appeared to be quite swollen. They were not considered to be gasping at the surface and there were no obvious haemorrhagic lesions.

Physical examination

Both goldfish were considered to be in good physical condition. No haemorrhages or ulcers could be seen. The gills appeared pale and clogged with thick grey mucus.

Post-mortem diagnosis examination

Initially a skin scrape was taken, and then both fish were euthanased with intravenous pentobarbitone (Fig.5.5). A post-mortem examination was then undertaken. The first goldfish weighed 179 g and had a standard length of 152 mm. The results for this first goldfish are:

Fig. 5.5 A skin scrape was taken and both fish were euthanased with intravenous pentobarbitone.

Gill squash

Huge numbers of these parasites were found

Normal gill lamellar architecture disrupted. Significant clubbing of lamellae

1. What are these parasites likely to be?

The parasites were identified as gill flukes – Dactylogyrus spp. They are readily distinguished from Gyrodactylus (skin flukes) by the characteristic four eye spots, plus Gyrodactylus are livebearers and the unborn fluke can frequently be seen inside the body of the adult. It was noted that the occasional protozoa Ichthyobodo spp. was seen at 100× magnification. Site of discovery is no real clue to identification – gill flukes, as in this case, will happily spread on to and survive on the skin, while skin flukes can occasionally infect the gills.

2. Why is it important to distinguish between Dactylogyrus and Gyrodactylus?

On examination of the coelomic cavity, the fish was revealed to be female with well-developed ovaries showing evidence of asynchronous egg development. The carcass was very fatty and the caudal kidney appeared very soft with a loss of normal texture. The spleen appeared enlarged (Fig.5.6).

Fig. 5.6 Post-mortem examination. The fish was a female with well-developed ovaries. The carcass was very fatty and the caudal kidney appeared very soft with loss of normal texture. The spleen appeared enlarged.

The second goldfish weighed 151 g, and had a standard length of 162 mm and had a similar presentation.

To investigate the possibility of underlying disease, the following samples were taken from the first goldfish and submitted for histopathology:

• Heart

• Gills

• Hepatopancreas

• Spleen

• Head kidney.

Histopathology results

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